Former world champion Parker produced a positive sample during a anti-doping examination administered on the day of his 11th-round stoppage versus British heavyweight Ipswich-born Wardley.
Wardley together with Joseph Parker participated in a thrilling contest held in London on 25 October to decide the next next in line for the WBO facing undisputed world heavyweight champion Oleksandr Usyk.
Joseph Parker had positioned himself as the primary candidate to challenge Oleksandr Usyk following compiling a remarkable six consecutive victories, but placed his shot at the title in jeopardy in London and suffered an 11th-round defeat.
A routine test given to Parker through Vada the day of the match came back positive and leaves the 36-year-old facing a challenge to demonstrate his cleanliness.
Parker's promotional company released an announcement stating: "Vada alerted all required parties regarding Joseph Parker had a positive result following a drug screening administered on the 25th October. During the ongoing inquiry, no additional comment will be made for now."
The New Zealand boxer was crowned titleholder back in 2016 prior to he lost his championship belt through a points decision versus Anthony Joshua in Cardiff two years later.
The fighter has been an active participant in the UK from that point, having eight matches altogether in Britain and transferring to Dublin for preparation alongside highly regarded trainer Andy Lee in recent years.
Under the tutelage of Lee, the boxer bounced back from his 2022 loss against Joe Joyce to chalk up several successes positioning him as the top contender to challenge Usyk before he lost against Wardley.
Following the boxer produced a failed test when he fought Wardley, allegedly for cocaine, an inquiry regarding the results has been started.
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